1. Field of the Invention
The present invention relates to ion flow glow plugs and systems for ignition and ion flow measurement using such glow plugs.
2. Description of Related Art
Ion flow measurement in the combustion space of a cylinder delivers various data on the progress of combustion. In an engine with several cylinders, this ion flow measurement can be taken in one, in several or in all cylinders. A system for ignition and ion flow measurement requires special glow plugs and a special control device which, as before, controls not only the ignition process, but also makes available an auxiliary voltage UH which can be applied to the glow plugs and takes the ion flow measurement. The glow plugs must be made such that, at least in the area of the glow plug tips, they represent a measurement electrode to which an auxiliary voltage UH can be applied. This voltage is then between the electrode and the inside wall of the cylinder. If at this point ions are produced by the combustion process, current flows. Its behavior allows conclusions regarding the combustion process in the cylinder. Preferably, the glow plug is made such that parts of the heater projecting into the cylinder can also be used as an electrode. That is, the heater and electrode are electrically coupled to one another.
For purposes of explanation, in the following, a system from the prior art is described using FIG. 1, the reference numbers having the following meaning:
(1) Glow plug with electrically insulated heater
(2) Electrode for ion flow measurements, can be made as a closed tube and can contain a heater (3)
(3) Heater, on one side electrically connected anywhere to the electrode (2)
(4) Plug body, electrically insulated relative to the electrode (2)
(5) Electrical insulation
(6) Electrical terminal, heavy current contact
(7) Solid-state switch, for example, n-channel MOS-FET transistor
(8) Voltage evaluation circuit
(9) Ground connection of the plug body (4) to the engine block
(10) Control device
(11) Supply voltage terminal UB, power feed
(12) Ground terminal, power removal
(13) Glow plug terminal, current to the glow plug
(14) Glow plug terminal, current return from the glow plug
(15) Control unit
(16) Switching stage for ignition current IGK 
(17) Switching stage for ion flow measurement
(18) Control signal for xe2x80x9cignitionxe2x80x9d function
(19) Control signal for xe2x80x9cion flow measurementxe2x80x9d function
(20) Auxiliary voltage generation UH 
A prior art bipolar ion flow measurement glow plug has the following features, as shown in FIG. 3:
Glow plug with 2 electrical terminals (6)
The electrode (2) and heater (3) are electrically insulated relative to the engine block by the plug body (4) which contains an insulating element (5)
The electrode (2) is connected anywhere to one of the two terminals of the heater (3)
The ignition current flows via the two electrical terminals (6)
For ion flow measurement the auxiliary voltage UH is applied to one of the two terminals (6), the other terminal remains unwired.
A previously known, conventional system (FIG. 1) has a number Nz of glow plugs (1) and a control device (10); Nz is the number of cylinders of the respective engine. To be able to use one, several or all Nz glow plugs (1) for ion flow measurement, special ion flow measurement glow plugs are needed in which the electrode (2) and the heater (3) are electrically insulated with respect to plug body (4). These glow plugs have two electrical terminals (6) with which the glow plugs are connected to a control device (10).
The control device (10) contains a control unit (15) which controls all functions; preferably, a microprocessor is used here. Nz glow plugs (1) can be connected to the control device (10). For each glow plug (1), there is a switching stage for the ignition current IGK (16) and in addition, when the ion flow is to be measured with the glow plug, there is a switching stage for ion flow measurement (17). Each glow plug (1) which is also used for ion flow measurement is connected via two terminals (13) and (14) to the two switching stages (16) and (17). Each switching stage is triggered by a control signal for the xe2x80x9cignitionxe2x80x9d (18) function or a control signal for the xe2x80x9cion flow measurementxe2x80x9d (19) function. During ion flow measurement, the xe2x80x9cignitionxe2x80x9d function is inactive. The switching stage (16) separates the glow plug (1) galvanically from the supply voltage terminal (11) and the ground terminal (12); at the same time, an auxiliary voltage UH for ion flow measurement is applied via the switching stage (17) to the glow plug (1) connected as a measurement electrode, and the ion flow measurement is taken.
During the ignition process, the current IGK flows through each switching stage (16) and each glow plug (1). For the circuit shown in FIG. 1, the current path is, for example, the following:
(11)xe2x86x92(16)xe2x86x92(13)xe2x86x92(6)xe2x86x92(3)xe2x86x92(2)xe2x86x92(6)xe2x86x92(14)xe2x86x92(16)xe2x86x92(12)
Mainly, when all glow plugs (1) are also being used for ion flow measurement, this means that a multiple of the current IGK is flowing via the supply voltage terminal (11) and the ground terminal (12), specifically a current Nz*IGK increased by a factor N2, the number of cylinders. This results in a very high current loading of these two terminals. For example, for an 8 cylinder engine, at a glow plug current IGK=30 A, the total current is 240 A by the two terminals (11) and (12).
The above described conventional system structure for ignition and ion flow measurements has several serious defects.
The glow plugs used for ion flow measurement must be bipolarly connected; a new connector system is necessary on the glow plug. A corresponding plug connector must have two heavy current contacts and is thus clearly more expensive than the unipolar version.
Plugging a bipolar mating connector onto the glow plug mounted in the engine block is more complex than inserting a rotationally symmetrical plug.
Return of the glow plug current to the control device requires a second heavy current line with a large cable cross section with a corresponding plug connection on the control device: Additional costs in the control device and due to the additional cable.
The second heavy current line together with the resulting additional contact points increases the unwanted contact resistances, and thus, reduces the voltage on the glow plug.
In the control device, in addition to the already present heavy current terminal in the positive line (current load: sum of all glow plug currents), which is usually made as a screw terminal, another heavy current terminal in the minus line is necessary: additional costs and additional effort in installation.
A primary object of the present invention is, therefore, to provide ion flow glow plugs and systems for ignition and ion flow measurement using such glow plugs which overcomes the shortcomings of the prior art.
This object is achieved in accordance with the invention by an ion flow measurement glow plug with an electrical terminal for the ignition current of a heating element which is located in a glow tube in the combustion space, the glow tube being located in a plug housing, insulated relative to the latter, and the plug housing being electrically connected to the engine block, having a solid-state switch integrated or modularly arranged at the terminal-side area of the plug, the solid-state switch being triggered by a control signal, and switching the second terminal of the heating element via the plug housing to the engine block (ground).
These and further objects, features and advantages of the present invention will become apparent from the following description when taken in connection with the accompanying drawings which, for purposes of illustration only, show several embodiments in accordance with the present invention.